Here are the amount of career wins Bisping's victims have gotten after he beat them
Hendo: 0
Silva: 1 (a robbery win at that)
Leites: 2
Dollaway: 1
Le: 0
Belcher: 0
Stann: 0
Miller: 0
Rivera: 1
Akiyama: 1
And the thing is that most of these victories aren't that decisive. Hendo/Silva/Leites were all coinflips that Bisping won at home, CB Dollaway gave him the business in round 1 and almost caught him in rd 3 even after getting KO'd by Machida's corpse. And everything preceding that were against guys on the way out the door.
Sure he's been active and he's been winning, but he wasn't that good in his prime and he hasn't been performing well in the wins. He merely has a luckbox that has been carrying him through and masking his age. He looked like complete ass vs Hendo and frankly wasn't great in any of the prior fights, and has aged 13 months since.
I can't imagine anybody actually wanting to bet on Bisping. The dude is trash.
Does this REALLY matter? I don't see a shred of evidence that it does. He has had plenty of time to train for this fight, and he is training intelligently with access to top notch resources. Ring rust isn't a real thing.